Influence of Ga flux on the growth and electron transport properties of AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy
TL;DR: In this article, the growth and electrical properties of the Al 0.15 Ga 0.85 N/GaN two-dimensional electron gas (2DEG) were studied for a range of III/V ratios during growth.
About: This article is published in Journal of Crystal Growth.The article was published on 2001-12-01. It has received 18 citations till now. The article focuses on the topics: Molecular beam epitaxy.
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Rohm1
TL;DR: In this paper, the authors have grown nitrogen-doped MgxZn1−xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy.
Abstract: We have grown nitrogen-doped MgxZn1−xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy. As N-sources, we employed NO-plasma or NH3 gas itself. As x increased, optimum growth temperature window for smooth film morphology shifted to higher temperatures, while maintaining high N-concentration (∼1×1019 cm−3). The heterosructures of MgxZn1−xO:N (0.1≤x≤0.4)/ZnO were fabricated into light emitting diodes of 500-μm-diameter. We observed ultraviolet near-band-edge emission (λ∼382 nm) with an output power of 0.1 μW for a NO-plasma-doped LED and 70 μW for a NH3-doped one at a bias current of 30 mA.
191 citations
TL;DR: In this paper, a "modulated growth" technique has been introduced to achieve large area uniformity and surface morphology control during rf plasma assisted molecular beam epitaxy of GaN, which consists of modulating the surface coverage of Ga through short-period shuttering of Ga, N, or Ga and N together to achieve alternating high and low surface coverages of Ga on the (0001) GaN surface.
Abstract: A “modulated growth” technique has been introduced to achieve large area uniformity and surface morphology control during rf plasma assisted molecular beam epitaxy of GaN. The technique consists of modulating the surface coverage of Ga through short-period shuttering of Ga, N, or Ga and N together (e.g., 50–100A growth periods), to achieve alternating high and low surface coverages of Ga on the (0001) GaN surface. The periods of growth with high Ga flux provide saturation coverage of Ga (∼2.5 ML Ga plus Ga droplets) over the full wafer, while the subsequent growth with low Ga flux facilitates a time-averaged Ga flux which is just below the crossover for droplet formation at the growth temperature. The growth transients in the Ga droplet regime are necessary to maintain smooth, pit-free surface morphologies, and the subsequent growth with low Ga flux suppresses droplet buildup over time. The process is monitored in situ utilizing reflection high energy electron diffraction and line-of-sight quadrupole mass spectroscopy. Results are presented which demonstrate that this approach is an effective means to achieve uniform surfaces over both 1∕4 and 2in. wafer sizes during nonbonded growth. The effects of temperature nonuniformities were mitigated and a surface free of both pitting and droplets has been realized over large areas.
54 citations
TL;DR: In this article, high resolution X-ray diffraction, cathodoluminescence (CL) and secondary mass spectrometry (SIMS) were used to characterize Al 0.82 In 0.18 N at 335nm.
49 citations
07 Nov 2002
TL;DR: State-of-the-art Mg doping profiles and transport properties have been achieved in MBE-derived p-type GaN, and the Mg-memory effect, and heterogeneous growth, substrate uniformity, and flux control are significant challenges for MOVPE and MBE.
Abstract: Metal-organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are the principal techniques for the growth and n-type (Si) and p-type (Mg) doping of III-nitride thin films on sapphire and silicon carbide substrates as well as previously grown GaN films. Lateral and pendeoepitaxy via MOVPE reduce significantly the dislocation density and residual strain in GaN and AlGaN films. However tilt and coalescence boundaries are produced in the laterally growing material. Very high electron mobilities in the nitrides have been realized in radio-frequency plasma-assisted MBE GaN films and in two-dimensional electron gases in the AlGaN/GaN system grown on MOVPE-derived GaN substrates at the crossover from the intermediate growth regime to the droplet regime. State-of-the-art Mg doping profiles and transport properties have been achieved in MBE-derived p-type GaN. The Mg-memory effect, and heterogeneous growth, substrate uniformity, and flux control are significant challenges for MOVPE and MBE, respectively. Photoluminescence (PL) of MOVPE-derived unintentionally doped (UID) heteroepitaxial GaN films show sharp lines near 3.478 eV due to recombination processes associated with the annihilation of free-excitons (FEs) and excitons bound to a neutral shallow donor (D/spl deg/X).
46 citations
Cites background from "Influence of Ga flux on the growth ..."
...trical properties are realized when the growth is conducted at the cross over from the intermediate Ga-rich regime to the Ga-droplet regime [48]....
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TL;DR: In this article, the evolution of the Ga adlayer during plasma-assisted molecular-beam epitaxy of (0001) GaN as a function of both Ga flux and growth temperature was studied.
Abstract: We present a study of the evolution of the Ga adlayer during plasma-assisted molecular-beam epitaxy of (0001) GaN as a function of both Ga flux and growth temperature. In situ quadrupole mass spectrometry was used to quantitatively determine the adsorbed Ga coverage by monitoring its subsequent desorption after GaN growth. Independent of the growth time, the Ga adlayer was found to form steady-state coverages that increase continuously from 0 to 2.5 monolayers when raising the Ga flux from N-rich to moderate Ga-rich growth conditions. At higher Ga fluxes or lower growth temperatures, macroscopic Ga droplets form on top of the Ga adlayer (Ga droplet regime). Based on the temperature dependency for the transition between the Ga adlayer and Ga droplet regime, we determined an apparent activation energy of 3.4eV, which is discussed with respect to previously reported values.
42 citations
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TL;DR: The surface morphologies of GaN grown by plasma-assisted molecular beam epitaxy under various growth conditions have been investigated in this article, where three growth regimes (one N stable and two Ga stable) are identified on a surface structure diagram (Ga/N ratio versus substrate temperature).
Abstract: The characteristic surface morphologies of GaN grown by plasma-assisted molecular beam epitaxy under various growth conditions have been investigated. Three growth regimes (one N stable and two Ga stable) are identified on a surface structure diagram (Ga/N ratio versus substrate temperature). The boundary between the N-stable regime (low Ga/N ratios) and the two Ga-stable regimes (high Ga/N ratios) is determined by the growth rate of the films and is constant over the range of substrate temperatures investigated. The boundary between the two Ga-stable regimes (the Ga-droplet regime and the intermediate regime) is determined by the formation of Ga droplets and has an Arrhenius dependence with substrate temperature. The characteristic morphologies of films grown within each of these regimes are investigated using atomic force microscopy and transmission electron microscopy. N-stable films have rough, heavily pitted morphologies. Films grown within the intermediate phase have areas of flat surface between la...
470 citations
TL;DR: In this article, the formation of the 2DEG in unintentionally doped AlxGa1−xN/GaN (x⩽0.31) heterostructures grown by rf plasma-assisted molecular-beam epitaxy is investigated.
Abstract: The formation of the two-dimensional electron gas (2DEG) in unintentionally doped AlxGa1−xN/GaN (x⩽0.31) heterostructures grown by rf plasma-assisted molecular-beam epitaxy is investigated. Low-temperature electrical-transport measurements revealed that the two-dimensional electron gas density strongly depends on both the thickness of the AlGaN layer and alloy composition. The experimental results agree very well with the theoretical estimates of the polarization-induced 2DEG concentrations. Low-temperature electron mobility was found to be much higher in the structures with lower electron sheet densities. Interface roughness scattering or alloy disorder scattering are proposed to be responsible for this trend. A maximum mobility of 51 700 cm2/V s (T=13 K) was obtained in the Al0.09Ga0.91N/GaN structure with a two-dimensional electron gas density of 2.23×1012 cm−2.
405 citations
TL;DR: In this article, the structure, morphology, and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy on metalorganic chemical vapor deposition (MOCVD)-grown GaN “template” layers were investigated as a function of the group III/group V flux ratio during growth.
Abstract: The structure, morphology, and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy on metalorganic chemical vapor deposition (MOCVD)-grown GaN “template” layers were investigated as a function of the group III/group V flux ratio during growth GaN layers grown with a low III/V ratio (N-stable growth) displayed a faceted surface morphology and a tilted columnar structure with a high density of stacking faults In contrast, films grown with a high III/V ratio (Ga-stable growth) displayed comparable structure to the underlying MOCVD-grown template The transition from N-stable to Ga-stable growth modes was found to occur over a narrow range of Ga fluxes at a growth temperature of 650 °C Evidence of Ga accumulation and step-flow growth was observed for films grown under Ga-stable conditions, leading to the formation of spiral growth features at the surface termination of mixed edge/screw dislocations Photoluminescence measurements indicate that the deep-level (∼550 nm) emission is
378 citations
TL;DR: In this article, the surface morphology of GaN films grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) was studied using atomic force microscopy (AFM).
Abstract: The surfaces of GaN films grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were studied using atomic force microscopy (AFM). Due to the high dislocation densities in the films (108 cm−2), the typical surface morphologies of layers grown by both techniques were dominated by three dislocation mediated surface structures—pinned steps, spiral hillocks, and surface depressions. The characteristics of these surface structures were found to depend on growth technique (MOCVD vs MBE) and the group-III to group-V ratio used in the growth of MBE GaN films. Pinned steps, created by the intersections of mixed character dislocations with the free surface, were found on all GaN films. The pinned steps were observed to be predominantly straight on the MOCVD GaN and curved into spiral hillock formations on the MBE GaN. Spiral growth hillocks form when pinned steps grow outward and around the dislocation under step-flow growth conditions. The tightness of the spiral hillocks on MBE G...
368 citations
TL;DR: In this paper, recent progress of AlGaN/GaN-based power high-electron-mobility transistors (HEMT's) is reviewed, and remarkable improvement in performances was obtained through adoption of high Al contents in the AlGAN layer.
Abstract: In this paper, recent progress of AlGaN/GaN-based power high-electron-mobility transistors (HEMT's) is reviewed. Remarkable improvement in performances was obtained through adoption of high Al contents in the AlGaN layer. The mobility in these modulation-doped structures is about 1200 cm/sup 2/.V/sup -1/.s/sup -1/ at 300 K with sheet densities of over 1/spl times/10/sup 13/ cm/sup -2/. The current density is over 1 A/mm with gate-drain breakdown voltages up to 280 V. F/sub t/ values up to 52 GHz have been demonstrated. Continuous wave (CW) power densities greater than 3 W/mm at 18 GHz have been achieved.
241 citations